1. Field of the Invention
This invention relates to an electron emission device, a display device, and methods for manufacturing them. More particularly, the invention relates to an electron emission device comprising fine particles of an electron emission body obtained by terminating carbon bodies grown on metal fine particles, serving as nuclei, with a low-work-function material via oxygen, a display device using such devices, and a method for manufacturing the electron emission device.
2. Description of the Related Art
Two types of electron emission devices, i.e., thermionic emission devices, and cold-cathode electron emission devices, have been known. The cold-cathode electron emission devices include field-emission-type electron emission devices, metal/insulator/metal-type electron emission devices, surface-conduction-type electron emission devices, semiconductor-type electron emission devices and the like.
As an example of the semiconductor-type electron emission devices, there is a device developed by Gorkom and others in which a reverse-biased strong electric field is applied to a p/n semiconductor, and electrons are emitted utilizing an avalanche phenomenon. As an example of the field-emission-type electron emission devices, a device described in C. A. Spindt, "Physical property of thin film field emission cathodes with molybdenum cones", J. Appl. Phys., 47, 5248 (1976) is known.
As the field-emission-type electron emission device, a Spindt-type field-emission device including an electron emission body, having a three-dimensionally sharpened distal end, disposed on a conductive substrate, and an electrode called a gate electrode having an aperture for drawing electrons from the electron emission body into a vacuum by generating a high electric field of about 10.sup.7 V/cm with the distal end of the electron emission body is generally used.
In order to form an image display device, an anode including a phosphor is disposed on an upper surface provided in a direction perpendicular to the substrate. Such an image display device performs display by causing electrons to impinge onto the phosphor to produce light emission by applying a voltage to the anode. Among the field-emission-type electron emission devices, there is a device in which a metal film is two-dimensionally processed into the shape of a triangle or a rectangle, and electrons are emitted from the obtained distal end or corner portion in parallel to a substrate by the electric field between facing electrodes provided on the substrate. Such a device is generally called a lateral-field-emission-type electron emission device.
In these conventional field-emission-type electron emission devices, since the distal end of an electron emission body is sharpened to concentrate the electric field thereon and a high electric field is applied in order to emit electrons, the use of a high-melting-point metallic material which resists against heat and electric field, such as W, Mo or the like, for the electron emission device has been studied. In such a material, there is the problem that the electron emission current changes with time due to deformation of the shape of the distal end of the electrion emission body, i.e., the problem of degradation. Recently, there have been proposals of providing emission current with a low electric field without sharpening the electron emission body by using diamond or the like having a low work function or a negative electron affinity as the electron emission body. Such proposals have been announced, for example, in C. Xie: SID International Symposium Digest Technical paper, pp. 43 (May, 1994), and U.S. Pat. No. 5,180,951.
In U.S. Pat. No. 5,463,271, there is disclosed that electron emission characteristics are improved by providing a low work function by chemically bonding Cs, K, Na, Ba or the like in an electrically positive state using oxygen or fluorine in an electrically negative state on at least 50% of the surface of carbon, preferably, conductive diamond.
Furthermore, there is an attempt to provide a color flat panel by arranging a plurality of these electron emission devices and combining them with a phosphor. In such a flat panel, a plurality of electron emission devices are disposed on a substrate so as to correspond to respective pixels of the phosphor. In order to perform gradation display by selecting arbitrary electron emission devices and controlling the amounts of electron emission of respective devices in accordance with an image signal, the arrangement of the electron emission devices, the phosphor and control electrodes have been devised. For example, as for the above-described semiconductor-type electron emission devices, there is an attempt such that electron emission devices provided on a semiconductor substrate are arranged in the form of a matrix while being combined with control electrodes, and arbitrary electron emission devices are selected and the amounts of electrons are controlled.
In the above-described Spindt-type devices, row-direction wirings are provided on a substrate, electron emission devices are provided on the row-direction wirings, control electrodes (the above-described gate electrodes) orthogonal to the row-direction wirings are provided in the column direction, and the amount of electron emission is controlled while selecting an electron emission device positionded at the cross point of a row-direction wiring and a column-direction wiring. By accelerating electrons drawn in a vacuum to impinge onto an anode having a phosphor disposed so as to face the substrate, a display device for emitting light from the phosphor is obtained.
In the literature by C. Xie cited above in which diamond or the like having a low work function or a low electron affinity is used, and U.S. Pat. No. 5,449,970, display devices are disclosed in which row-direction wirings are provided on a substrate, a phosphor facing the substrate is provided on column-direction wirings, diamond thin films are partially provided on the row-direction wirings at respective cross points of the row-direction wirings and the column-direction wirings, and electron emission devices are selected and controlled.
However, among the above-described electron emission devices, the Spindt-type device has the problem that it is difficult to reproducibly perform three-dimensional processing of sharpening the distal end of the electron emission body from the viewpoint of mass production capability. In addition, since it is necessary to perform very-fine submicron-order processing of the aperture of the gate electrode in order to perform modulation at a lower voltage, there is a problem in reproducibility. In the case of using diamond as the electron emission body, the above-described unique display panel can be provided because diamond has a low work function or a negative electron affinity and can therefore emit electrons at a low electric field. However, since diamond, serving as the electron emission body, is formed according to laser ablation or the like, there arise problems of difficulty in obtaining a large area, controllability of the shape and the density of diamond, control of the physical properties of the surface of diamond, and the like, thereby causing a problem in uniformity. Hence, this type of device is not yet practically used.